WO2004048991A1 - Determination of subencoding mri coil sensitivities in a lower order magnetic field - Google Patents
Determination of subencoding mri coil sensitivities in a lower order magnetic field Download PDFInfo
- Publication number
- WO2004048991A1 WO2004048991A1 PCT/IB2003/005317 IB0305317W WO2004048991A1 WO 2004048991 A1 WO2004048991 A1 WO 2004048991A1 IB 0305317 W IB0305317 W IB 0305317W WO 2004048991 A1 WO2004048991 A1 WO 2004048991A1
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- WO
- WIPO (PCT)
- Prior art keywords
- region
- homogeneity
- full
- measured
- sensitivity
- Prior art date
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/561—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
- G01R33/5611—Parallel magnetic resonance imaging, e.g. sensitivity encoding [SENSE], simultaneous acquisition of spatial harmonics [SMASH], unaliasing by Fourier encoding of the overlaps using the temporal dimension [UNFOLD], k-t-broad-use linear acquisition speed-up technique [k-t-BLAST], k-t-SENSE
Definitions
- the invention relates to a magnetic resonance (MR) method for the imaging of an object from a plurality of signals acquired by an array of receiver antennae, whereas prior to imaging a sensitivity map of each of the receiver antennae is provided, at least tow adjacent antennae record signals originating from the same imaging position and the image intensity is calculated from the signals measured by the different antennae, and wherein the number of phase encoding steps is reduced with respect to the full set thereof.
- MR magnetic resonance
- the invention also relates to an MR device and a computer program product for carrying out such a method.
- SENSE sensitivity encoding method
- the SENSE method is based on an algorithm which acts directly on the image as detected by the coils of the magnetic resonance apparatus and in which subsequent encoding steps can be skipped and hence an acceleration of the signal acquisition for imaging by a factor of from two to three can be obtained.
- Crucial for the SENSE method is the knowledge of the sensitivity of the coils arranged in so called sensitivity maps.
- the main magnet of the Philips NT with the Intera 1.5 T magnet has a quit sha ⁇ distinction between the inner region in which the main magnetic field is homogeneous and the outer region in which the main magnetic field is completely inhomogeneous.
- the inner region of high homogeneity is larger than the usual extent of the human body in the left-to-right direction which is orthogonal to the elongate direction of the magnet.
- the polynomial expansion of the main magnetic field is zero up to a high-order, which means that there is a quick transition between the inner region or volume of high homogeneity and the outer region of high inhomogeneity.
- SENSE For the set-up of SENSE it is required to provide a sensitivity map of the coils which is done by means of a large voxel gradient echo imaging or fast field echo scan (FFE), which is also known as coarse calibration scan (COCA).
- FFE fast field echo scan
- COCA coarse calibration scan
- a magnetic resonance imaging apparatus and technique exploits spatial information inherent in a surface coil array to increase MR image acquisition speed, resolution and/or field of view.
- the MR signal from a combination of coils having an aggregate sinusoidal and cosinusoidal spatial sensitivity profile have an information content somewhat different from that of the usual coil signal.
- By separating out one or more collected signals corresponding to pure spatial harmonics, these may be used to fill a larger portion of the data space than is done conventionally. Partial signals are thus acquired simultaneously in the component coils of the array and formed into two or more signals corresponding to orthogonal spatial representations.
- lines of the k-space matrix required for image production are formed using a set of separate linear combinations of the component coil signals to substitute for spatial modulations normally produced by phase encoding gradients.
- the combined MR signal from the inhomogeneous coils is thus shifted in k-space by a predetermined amount dependent from the spatial frequency of the inhomogeneous coil sensitivity.
- This k-space shift has precisely the same form as the phase- encoding shift produced by evolution in a y gradient.
- This method is specifically designed for SMASH. However, it does not give any further indication to solve the problem of using SENSE with designs of main magnet of lower order as discussed above.
- This object of the invention are achieved by a method as defined in Claim 1.
- the invention is further related to an apparatus as defined in Claim 6 and to a computer program product as defined in Claim 7.
- the present invention has the main advantage that main magnets with a less sha ⁇ distinction between the inner region of high homogeneity and the outer region of complete inhomogeneity, i.e. magnets of lower order, now can be used also for the above mentioned SENSE method.
- Fig. 1 an MR image of a patient with an interesting organ
- Fig. 2 an MR imaging system for carrying out the method of the present invention.
- the region of high homogeneity is relatively large; in particular, it is larger than the usual extent of the human body in left/right direction.
- the inhomogeneity of the magnet system is such high that no sensible signals can be collected. If the magnetic field is vanishing to zero, it is per definition also fully inhomogeneous.
- a second region 20 between dashed line 18 and the dotted line 19 is of moderate inhomogeneity, i.e. the region within which the SENSE-scan is still able to collect any meaningful signal.
- the margin between the dashed line 18 and the dotted line 19 is typically about 20 mm wide.
- the problem area is the intermediate region 20, in which an image is performed by the SENSE-scan and which is possibly folded over an interesting region. However, the reference scan cannot reveal it and hence the system has no knowledge on coil-sensitivities in that region.
- the system is designed in such a way that knowledge on expected field inhomogeneities (or their variations) are explicitly known for all locations within the magnet bore. From that knowledge (and knowing the properties of the COCA scan), a figure indicating the "reliability of sensitivity information" can be derived for every point within the magnet bore. In the COCA scan, the sensitivity information is measured. In the high- homogeneity region it is accurate but elsewhere it is not. The knowledge on where this information is reliable allows for an extrapolation scheme which consists of the following smoothing algorithm: on each position, i.e.
- an estimate of coil sensitivities is derived by a weighted addition of the measured sensitivities of the region around that point; the weights depend on a) The distance between the point and points in its direct neighborhood. b) The reliability of the information at neighboring points.
- s c (x, y, z) is the estimate of sensitivity of coil c at position (x, y, z); the measured value of coil sensitivity is s.
- the function D is a monotonically decreasing function of distance (e.g. (distance + constant) -0 , with the power p preferably larger than 2).
- the reliability function r is derived from the knowledge of the field inhomogeneity; more specifically, it is preferably a function that is 1 in case of high homogeneity and 0 in regions with high inhomogeneity, e.g.,
- Fig. 2 A practical embodiment of an MR device is shown in Fig. 2, which includes a first magnet system 2 for generating a steady magnetic field, and also means for generating additional magnetic fields having a gradient in the X, Y, Z directions, which means are known as gradient coils 3.
- the Z direction of the co-ordinate system shown corresponds to the direction of the steady magnetic field in the magnet system 2 by convention, which only should be linear.
- the measuring co-ordinate system x, y, z to be used can be chosen independently of the X, Y, Z system shown in Fig. 2.
- the gradient coils 3 are fed by a power supply unit 4.
- An RF transmitter coil 5 serves to generate RF magnetic fields and is connected to an RF transmitter and modulator 6.
- a receiver coil is used to receive the magnetic resonance signal generated by the RF field in the object 7 to be examined, for example a human or animal body.
- This coil 5 represents an array of multiple receiver antennae.
- the magnet system 2 encloses an examination space which is large enough to accommodate a part of the body 7 to be examined.
- the RF coil 5 is arranged around or on the part of the body 7 to be examined in this examination space.
- the RF transmitter coil 5 is connected to a signal amplifier and demodulation unit 10 via a transmission/reception circuit 9.
- the control unit 11 controls the RF transmitter and modulator 6 and the power supply unit 4 so as to generate special pulse sequences which contain RF pulses and gradients.
- the control unit 11 also controls detection of the MR signal(s), whose phase and amplitude obtained from the demodulation unit 10 are applied to a processing unit 12.
- the control unit 11 and the respective receiver coils 3 and 5 are equipped with control means to enable switching between their detection pathways on a sub-repetition time basis (i.e. typically less than 10 ms).
- These means comprise inter alia a current/voltage stabilization unit to ensure reliable phase behavior of the antennae, and one or more switches and analogue-to-digital converters in the signal path between coil and processing unit 12.
- the processing unit 12 processes the presented signal values so as to form an image by transformation. This image can be visualized, for example by mearis of a monitor 13.
Abstract
Description
Claims
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US10/536,284 US7330575B2 (en) | 2002-11-26 | 2003-11-20 | Determination of subencoding MRI coil sensitivities in a lower order magnetic field |
AU2003280119A AU2003280119A1 (en) | 2002-11-26 | 2003-11-20 | Determination of subencoding mri coil sensitivities in a lower order magnetic field |
JP2004554824A JP2006507072A (en) | 2002-11-26 | 2003-11-20 | Determination of MRI coil sensitivity in low-order magnetic fields |
EP03772498A EP1567880A1 (en) | 2002-11-26 | 2003-11-20 | Determination of subencoding mri coil sensitivities in a lower order magnetic field |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP02079910.2 | 2002-11-26 | ||
EP02079910 | 2002-11-26 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2004048991A1 true WO2004048991A1 (en) | 2004-06-10 |
Family
ID=32338106
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/IB2003/005317 WO2004048991A1 (en) | 2002-11-26 | 2003-11-20 | Determination of subencoding mri coil sensitivities in a lower order magnetic field |
Country Status (5)
Country | Link |
---|---|
US (1) | US7330575B2 (en) |
EP (1) | EP1567880A1 (en) |
JP (1) | JP2006507072A (en) |
AU (1) | AU2003280119A1 (en) |
WO (1) | WO2004048991A1 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2012001583A1 (en) * | 2010-07-02 | 2012-01-05 | Koninklijke Philips Electronics N.V. | Parallel magnetic resonance imaging using undersampled coil data for coil sensitivity estimation |
JP2016086991A (en) * | 2014-10-31 | 2016-05-23 | 株式会社東芝 | Magnetic resonance imaging apparatus |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN102576061B (en) | 2009-10-02 | 2015-07-22 | 皇家飞利浦电子股份有限公司 | MR imaging using multi-channel RF excitation |
US9146293B2 (en) | 2012-02-27 | 2015-09-29 | Ohio State Innovation Foundation | Methods and apparatus for accurate characterization of signal coil receiver sensitivity in magnetic resonance imaging (MRI) |
EP3557276A1 (en) * | 2018-04-16 | 2019-10-23 | Siemens Healthcare GmbH | Method and control device for producing magnetic resonance images within and outside of the homogeneous region of the b0-field |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5910728A (en) * | 1996-11-12 | 1999-06-08 | Beth Israel Deaconess Medical Center | Simultaneous acquisition of spatial harmonics (SMASH): ultra-fast imaging with radiofrequency coil arrays |
Family Cites Families (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE4444061A1 (en) | 1994-12-10 | 1996-06-13 | Philips Patentverwaltung | MR method for determining the nuclear magnetization distribution with a surface coil arrangement |
AT406092B (en) * | 1995-08-28 | 2000-02-25 | Szeles Josef Constantin Dr | METHOD AND DEVICE FOR FORMING AN IMAGE WITH NUCLEAR SPIN RESONANCE |
EP0990169A1 (en) * | 1998-04-17 | 2000-04-05 | Koninklijke Philips Electronics N.V. | Magnetic resonance imaging method and apparatus |
US6680610B1 (en) | 1999-05-24 | 2004-01-20 | Walid E. Kyriakos | Apparatus and method for parallel MR data acquisition and parallel image reconstruction from multiple receiver coil arrays for fast MRI |
AU1811201A (en) | 1999-12-03 | 2001-06-12 | Johns Hopkins University, The | Apparatus and methods for spatial encoded mri |
US6777934B2 (en) * | 1999-12-08 | 2004-08-17 | Hitachi Medical Corporation | Magnetic resonance imaging method and apparatus |
US6717406B2 (en) | 2000-03-14 | 2004-04-06 | Beth Israel Deaconess Medical Center, Inc. | Parallel magnetic resonance imaging techniques using radiofrequency coil arrays |
US6771071B1 (en) * | 2001-11-06 | 2004-08-03 | The Texas A&M University System | Magnetic resonance imaging using a reduced number of echo acquisitions |
US6903551B2 (en) * | 2002-05-01 | 2005-06-07 | Brigham & Women's Hospital, Inc. | Variable-density parallel magnetic resonance imaging |
US6919722B2 (en) * | 2003-10-09 | 2005-07-19 | Ge Medical Systems Global Technology Company, Llc | Image quality improvement for SENSE with low signal regions |
-
2003
- 2003-11-20 EP EP03772498A patent/EP1567880A1/en not_active Withdrawn
- 2003-11-20 JP JP2004554824A patent/JP2006507072A/en not_active Ceased
- 2003-11-20 AU AU2003280119A patent/AU2003280119A1/en not_active Abandoned
- 2003-11-20 US US10/536,284 patent/US7330575B2/en not_active Expired - Fee Related
- 2003-11-20 WO PCT/IB2003/005317 patent/WO2004048991A1/en active Application Filing
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5910728A (en) * | 1996-11-12 | 1999-06-08 | Beth Israel Deaconess Medical Center | Simultaneous acquisition of spatial harmonics (SMASH): ultra-fast imaging with radiofrequency coil arrays |
Non-Patent Citations (3)
Title |
---|
M.A.G.BALLESTER ET AL.: "Robust Estimation of Coil Sensitivities for RF Subencoding Acquisition Techniques", PROC.INTL.SOC.MAG.RESON.MED. 9 (2001), pages 799, XP002270526 * |
MURAKAMI J W ET AL: "INTENSITY CORRECTION OF PHASED-ARRAY SURFACE COIL IMAGES", MAGNETIC RESONANCE IN MEDICINE, ACADEMIC PRESS, DULUTH, MN, US, vol. 35, no. 4, 1 April 1996 (1996-04-01), pages 585 - 590, XP000587727, ISSN: 0740-3194 * |
PRUESSMANN K P ET AL: "SENSE: SENSITIVITY ENCODING FOR FAST MRI", MAGNETIC RESONANCE IN MEDICINE, ACADEMIC PRESS, DULUTH, MN, US, vol. 42, no. 5, November 1999 (1999-11-01), pages 952 - 962, XP000866655, ISSN: 0740-3194 * |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2012001583A1 (en) * | 2010-07-02 | 2012-01-05 | Koninklijke Philips Electronics N.V. | Parallel magnetic resonance imaging using undersampled coil data for coil sensitivity estimation |
JP2016086991A (en) * | 2014-10-31 | 2016-05-23 | 株式会社東芝 | Magnetic resonance imaging apparatus |
Also Published As
Publication number | Publication date |
---|---|
US20060058628A1 (en) | 2006-03-16 |
AU2003280119A1 (en) | 2004-06-18 |
US7330575B2 (en) | 2008-02-12 |
JP2006507072A (en) | 2006-03-02 |
EP1567880A1 (en) | 2005-08-31 |
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